This invention has relation to the mooring of floating vessels over predetermined locations on the floors of bodies of water. More specifically it relates to the rapid paying out and drawing in of extensive lengths of wire rope mooring lines under conditions of no load or low load, and the holding and more deliberate drawing in and paying out of such lines under conditions of very high loading on the lines.
It is known to anchor semi-submersible offshore drilling platforms in place utilizing elongated anchor lines extending out from such plaftforms in all directions. See U.S. Pat. No. 3,842,776 granted to Wudtke in October of 1974 and U.S. Pat. No. 4,020,779 granted to Kitt in May of 1977. See also U.S. Pat. No. 3,031,997, granted to Nesbitt in May of 1962; and U.S. Pat. Nos. 3,318,275 and 3,349,740, the first granted to Field in May of 1967 and the second granted to him in October of 1967.
Mooring lines stretching out in all directions from the bottom of a cylindrical opening passing from top to bottom through a central portion of an otherwise conventional ship are shown in U.S. Pat. No. 3,191,201 granted to Richardson et al in June of 1965.
U.S. Pat. No. 3,563,043 granted to Nelson in February of 1971 as well as all of the patents listed above were uncovered in a search of the prior art. The Nelson patent is not believed to be particularly pertinent to the present invention.
Semi-submersible oil exploration and drilling platforms include horizontal floats or pontoons which are entirely air-filled to cause the platforms to float on the surface of the water while they are being towed into place. In order to minimize the effects of oceans swells and waves on the platforms, the pontoons are submerged during use of the platforms for their intended purposes. This subjects only the main vertical support columns to the surface action of the sea.
Once a platform is in its desired position, the sea water can be let into the pontoons to achieve the desired submersion of the platform. Then in the process of fixedly mooring the platform, the water can be evacuated from the pontoons, leaving the mooring lines passing through fairleads located at lower portions of the platform to restrain the platform from rising as the pontoons become more and more buoyant. This has the effect of very positively and firmly fixing the positioning of the platform over a drilling point, for example, and very substantially diminishes the effects of surface action of the seas on the platform. After and as the pontoons are evacuated, extreme upward forces are being absorbed by the mooring lines.
In floating offshore drilling platforms and in similar vessels, deck space and other working space is at a premium. The economic effectiveness of a particular vessel is measured in proportion to the amount of space available to perform the primary function of the vessel (drilling for oil, for example) and in reverse proportion to the amount of space required for the necessary subsidiary functions (holding the vessel in place and handling and storing the mooring lines, for example).
As disclosed in Wudtke U.S. Pat. No. 3,842,776, a large winchdriven drum 38 has to be able to store all of the wire rope 40 before mooring and to transmit sufficient pull on the mooring line to keep the vessel semi-submerged. The drum 38 must be so large that it has to be mounted on the top of one of the support columns 30 of the offshore platform. The drum 38 must have a substantial distance between its end flanges so that the maximum pulling force needed can be developed without too many layers of wire wound on it. In other words, the radial distance between the outer strand or pulling strand of wire rope going onto the drum measured on the radius of the drum must be kept to a minimum in order to develop the necessary pulling forces where the winch is doing all of the pulling on the wire rope.
Linear pulling machines which operate on wire rope are well known. For example, such machines are sold under the trademark LUCKER by American Hoist & Derrick Company, Marine/Energy Division, 63 South Robert Street, St. Paul, Minn. 55107. See Lucker Catalog ME-L600, marked 10 MJR9-80, an earlier Catalog No. 500 entitled Lucker Manufacturing Company and marked 25 MJR477.
It is known to use storage reels to automatically wind up and store the wire rope coming from the linear pull machine. See the upper right-hand corner of page 5 of said Catalog No. 500.
What was needed before the present invention was a power operated winch which was compact enough so that it could be positioned at a location where it would not use up valuable deck and other work space. At the same time, a further power means was needed which could exert high forces on the mooring line to draw it in and pay it out under severe load conditions, and which could hold the line under static conditions even up to the tensile strength of the line itself, this further power means also taking up no deck space or other space useable for the primary mission of the vessel.
Applicants and those in privity with them are aware of no closer prior art than that discussed and disclosed above; and they are aware of no prior art which anticipates the claims herein.